This invention relates generally to a pressure responsive fluid shut-off device and, more particularly, to a device for shutting off a supply of liquid propane (LP) gas in the event that a malfunction in a supply system results in excessive gas pressures.
The appearance of excessive gas pressures in LP gas supply systems introduces substantial risk of fire and explosion. In most domestic LP gas systems, fire and explosion hazards are prevented by a regulator located between an LP gas supply tank and a supply line feeding appliances encompassed by the system. The regulator functions to reduce supply tank pressure, typically above 100 psi, to a safe line pressure of less than 1 psi. However, malfunctions in such regulators often lead to the appearance of hazardous gas pressures in supply lines. A common cause of regulator malfunction is a blockage of vent openings that establish atmospheric reference pressures in typical differential pressure responsive regulators. Upon loss of an accurate atmospheric pressure reference, a regulator can cease to function properly and in some instances, allow a hazardous increase in gas pressure. Also, under certain circumstances, low pressure liquid propane will leak through a regulator valve and then evaporate in the supply line creating hazardous gas pressure therein.
Many of the above problems are eliminated by a combined solenoid operated valve and shut-off device disclosed in U.S. Pat. No. 4,180,241 issued Dec. 25, 1979. That valve includes a magnetic plunger for cycling a valve closure between open and closed positions in response to an electrical signal and a shut-off mechanism activatable to lock the valve closure in its closed position in response to a predetermined fluid pressure at the inlet. Valve operation is provided by an actuator rod that is normally latched in a set position within the magnetic plunger and reciprocates therewith to produce the desired cycling of the valve closure. However, in response to an excessive inlet pressure, a piston moves the actuator rod relative to the plunger into a release position which locks the closure means in closed position and prevents any further gas flow. A resumption of gas flow requires actuation of the reset mechanism to move the plunger relative to the actuator rod so as to produce latching thereof into its set position and thereby permit reopening of the valve.
Although eliminating most of the problems associated with prior LP gas valves, the above mentioned valve and shut-off device exhibits one undesirable trait. A bias spring member produces a continuous force that tends to separate the magnetic plunger and actuator rod. This factor can sometimes cause inadvertent shut-off of the valve.
The object of this invention, therefore, is to provide an improved pressure responsive shut-off that eliminates the dangers associated with excessively high gas pressure in the supply lines of LP gas systems.